The U.S. government is intensifying its intelligence sharing and military consultations with Turkey behind the scenes as both countries confront the possibility that Syria’s civil conflict could escalate into a regional war, according to U.S. and NATO officials.

The Obama administration has said it wants to avoid getting drawn militarily into Syria and for months has resisted pressure from Arab allies and some Republicans to back Syria’s rebel groups more forcefully.

But as Syria’s internal conflict has increasingly spilled across its northern border into Turkey, the U.S. government has stepped up cooperation with its key NATO ally. In recent weeks, military officials from both countries have met to make contingency plans to impose no-fly zones over Syrian territory or seize Syria’s stockpiles of chemical and biological weapons, U.S. officials said.

U.S. intelligence agencies were also the source of a tip that led the Turkish military to intercept and ground a Syrian passenger plane en route from Moscow to Damascus last week on suspicions that it was carrying Russian-made military hardware, according to U.S. officials.

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U.S., Turkey discussing options in Syria

The Syrian plane was carrying “radar and electrical parts for Syria’s Russian-made antiaircraft systems,” one U.S. official said, speaking on the condition of anonymity to discuss details of the sensitive operation. Syria has relied on Russia for decades to help build its radar and antiaircraft defenses, among the most extensive in the Middle East.

The plane grounding sparked a diplomatic dust-up among Turkey, Russia and Syria and further exacerbated tensions that erupted Oct. 3 when Syria fired shells across the border and killed five Turkish civilians.

Since then, cross-border shelling has continued as the Syrian military has attacked rebel groups along the frontier, with rounds sometimes landing in Turkish territory. Turkey has retaliated with artillery strikes, most recently on Friday, while warning Damascus that the risk of all-out war is increasing.

“This week I know there is a special focus of our military experts talking about Syria. And what militaries do well is plan for every contingency and every eventuality.” Francis J. Ricciardone Jr., U.S. ambassador to Turkey

The United States and NATO have publicly supported Turkey, saying it has a right to act in self-defense. At the same time, they have called for restraint and repeated that neither Washington nor Brussels has any intention of getting involved militarily.

Behind the scenes, however, the border clashes have changed the strategic calculus and led U.S. military and intelligence officials in particular to collaborate more closely with Turkey.

“I can certainly assure you that our militaries, our military officers, are in contact,” Francis J. Ricciardone Jr. , the U.S. ambassador to Turkey, told journalists in Ankara on Tuesday. “This week I know there is a special focus of our military experts talking about Syria. And what militaries do well is plan for every contingency and every eventuality.”

Ricciardone said “no political decision has been made” regarding whether to support or impose a no-fly zone in Syrian territory to protect civilians or opponents of the government of Bashar alAssad in Damascus, but he acknowledged that U.S., Turkish and NATO officials were discussing options.

“Will we consider it?” he said. “We consider everything.”

Ricciardone did not provide details about the recent U.S.-Turkish military talks regarding Syria. But his comments came after Adm. James Stavridis, the chief of the U.S. European Command and the Supreme Allied Commander of NATO military forces, visited Ankara and Izmir in early October.

Stavridis did not speak with reporters, but he posted a message on his Facebook account saying that he met with Turkish Defense Minister Ismet Yilmaz and Gen. Necdet Ozel, Turkey’s top military commander, to hold “important talks considering the events transpiring in the Levant.”

A NATO official confirmed that Stavridis discussed the increasing volatility of the Turkish-Syrian border but said that Turkey has not made any formal requests for military assistance from either NATO or Washington.

For now, Turkey primarily wants statements of public support from NATO and reassurances that the alliance would come to its aid if necessary, said Ross Wilson, a former U.S. ambassador to Turkey who now serves as director of the Dinu Patriciu Eurasia Center at the Atlantic Council in Washington.

“A big part of what they’re looking for is that I’d call political support as opposed to NATO sending in fighter squadrons or thousands of troops,” Wilson said. But he added that Turkey also wants the U.S. and NATO to demonstrate willingness to update military preparations and planning in case events along the Syrian border quickly spiral out of control.

“In their eyes, there’s a whole bunch of scenarios that could result in outside involvement, but they don’t see anybody talking about it as much as they’d like,” Wilson said.

The Obama administration has said that it would likely intervene if Assad’s government engaged in chemical or biological warfare, and Pentagon officials have said they are monitoring the whereabouts of Syria’s stockpiles of those weapons.

With a presidential election looming, however, the administration has said it is pushing first for a political solution to the Syrian civil war. It has pressed the United Nations Security Council to take action, even though Russia and China, which hold veto power, have resisted.

With the United Nations paralyzed, Turkey may lean on NATO to intervene even without a U.N. mandate, possibly by imposing a no-fly zone or haven for Syrian refugees if the civil war worsens, said Soner Cagaptay, director of the Turkish Research Program at the Washington Institute for Near East Policy. More than 100,000 Syrian refugees have sought shelter in Turkey.

“NATO is the new U.N. for Ankara when it comes to Syria,” he said.

Greg Miller in Washington and Michael Birnbaum in Brussels contributed to this report.